property Chart.HistogramValue (Date as Variant, [Name as Variant], [Group as Variant]) as Double
Gets the value in the histogram at specified date-time, for giving type of bars or/and groups.

TypeDescription
Date as Variant A DATE expression that specifies the date-time being queried for its value in the control's histogram, or a s STRING expression such as "min" to get the minimum value excepts 0 in the histogram, and "max" to get the maximum value in the histogram. The min and max flags determines the minimum and maximum values from the displayed values not from the entire chart. The Date parameter should be a value between first and last visible date in the chart, else the HistogramValue property gets -1 result.
Name as Variant A String expression that specifies the name ( or a list of names separated by comma(,) character ) of the bar to be queried for its value in the histogram. The Name parameter has no effect, if the chart's histogram displays a single type of the bar in the histogram. The BarName parameter of the AddBar method or ItemBar(exBarName) value specifies the name of displayed bar. If Name parameter is missing or empty, all bars are queried. For instance, if the histogram displays the curves for multiple type of bars, the Name parameter indicates the name of the bars to be queried separated by comma(,) character. For instance, "Task,Summary" queries the values for Task or Summary bars.
Group as Variant A Long expression that specifies the index of the group of bars in the histogram to be queried, or a String expression that indicates the list of group(index) to be queried. The Group parameter has no effect, if the chart's histogram displays no groups in the histogram. Groups are usually displayed when your data is shown as a tree. If missing or empty, all groups are queried. For instance, "0,1" queries the values for first and second group of bars.
Double A DOUBLE expression that specifies the value of the specified type/bar, group and date-time in the histogram. The HistogramValue property returns -1 if any error occurs. For instance, the histogram is not visible, a date-time that's not visible in the control's client area, and so on.
The HistogramValue property returns valid values while the control displays the control's histogram. Currently, the HistogramValue property returns -1, if the chart displays no histogram ( HistogramVisible property is False, or HistogramHeight property is 0 ).

The following screen shot shows the histogram with a single task and with no grouping, where Name or Group parameters has no effect:

The following screen shot shows the histogram with a single task but with grouping ( 3 groups, United Package, Speedy Express, Federal Shipping ), where Name has no effect, instead Group parameter could be 0, 1, 2 ( empty or any combination of them )

The following screen shot shows the histogram for two tasks but with no grouping , where Name could be specified , instead Group parameter has no effect:

The following screen shot shows the histogram for two tasks but with grouping , where Name could be specified, and Group parameter could be 0, 1, 2 ( empty or any combination of them )